The proposed research is a continuation of work performed during the past years and concerns the processing of auditory signals in the middle and inner ear (cochlea), the cochlear nerve, and the ventral cochlear nucleus. The long-range purpose of the middle-ear research is to understand the mechanisms of sound transmission through it. Specifically, the work planned for the next project period deals with a further experimental and mathematical analysis of the stapedius-muscle reflex and aims at identification of its functional components. Such identification has applications in audiological testing and otological diagnostics. The experiments involved are based on measurements of acoustic impedance at the tympanic membrane. The planned cochlear research is two-pronged. One prong is oriented toward cochlear micromechanics and the other toward the inner hair cells. Both are potentially useful for early detection of developing cochlear damage and, as a consequence, for prevention of its further progress. Regarding the micromechanics, we have a conceptual and mathematical model that accounts for large bodies of mechanical and neural data obtained on normal and pathological cochleas. The model includes a key assumption derived from experiments on lizard auditory papillae. We plan to test it directly on mammalian cochleas. Confirmation of the assumption would mean that we understand the fundamental mechanical processes in the cochlea. This must appear desirable in the period of growing popularity of cochlear prosthetics. The electromechanical transduction in the inner hair cells begins the chain of neural events that continue through the cochlear nerve and the cochlear nucleus. The proposed microelectrode recordings of electrical signals at all these sites coupled with mathematical analysis endeavors to analyze the resulting neural characteristics into their functional and structural components. It must be obvious that association of functional elements with the structural ones is at the basis of medical diagnostics. Special emphasis is placed on the relation of neural elements to the resulting characteristics.